Syncthing failing to start on (L)ubuntu 20.04

Hi there,

On my (L)ubuntu box I can only get syncthing started if I reinstall it after each login.

What is the problem:

  • I have syncthing installed on both an Ubuntu PC and Arch laptop;
  • They are not syncing unless I have the browser interface open on the ubuntu box.
  • Syncthing on ubuntu worked fine after a reinstall, but failed to start on the next reboot.

What have I tried so far:

Purge and reinstall via apt followed by:

systemctl --user enable syncthing.service
systemctl --user start syncthing.service

then:

systemctl --user status syncthing.service

all fine - but after a reboot:

systemctl --user status syncthing.service returns:

● syncthing.service - Syncthing - Open Source Continuous File Synchronization
     Loaded: loaded (/usr/lib/systemd/user/syncthing.service; enabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Tue 2021-09-07 10:51:40 BST; 5min ago
       Docs: man:syncthing(1)
    Process: 12873 ExecStart=/usr/bin/syncthing serve --no-browser --no-restart --logflags=0 (code=exited, status=1/FAILURE)
   Main PID: 12873 (code=exited, status=1/FAILURE)

Sep 07 10:51:40 <user>  systemd[1573]: syncthing.service: Scheduled restart job, restart counter is at 4.
Sep 07 10:51:40 <user>  systemd[1573]: Stopped Syncthing - Open Source Continuous File Synchronization.
Sep 07 10:51:40 <user> systemd[1573]: syncthing.service: Start request repeated too quickly.
Sep 07 10:51:40 <user> systemd[1573]: syncthing.service: Failed with result 'exit-code'.
Sep 07 10:51:40 <user> systemd[1573]: Failed to start Syncthing - Open Source Continuous File Synchronization.

Fuller details (incl error messages) are on the Ubuntu forum, but those guys are not syncthing specialists and I’ve had no response.

Happy to post errors / outputs here directly.

So, following that link:

Sep 04 13:24:14 [USER] syncthing[4422]: [start] INFO: syncthing v1.18.1 "Fermium Flea" (go1.16.6 linux-amd64) deb@build.syncthing.net 2021-07-30 12:41:57 UTC [noupgrade]
Sep 04 13:24:14 [USER] syncthing[4422]: [start] WARNING: Error opening database: resource temporarily unavailable (is another instance of Syncthing running?)

It appears to already be running, for the same user.